With Tropical Cyclone Bune cruising by, perhaps it’s timely to stick with coastal issues another day.
Awhile back, I spent the morning on a ‘site visit’ with Larry Dallimore, a Westshore resident, to hear his case as to why ‘beach renourishment’ — the current strategy of the Napier and Regional Councils for dealing with erosion at Westshore — would never work.
I discovered that Larry isn’t a dilettante on the issues involved, although he seems to be treated as a meddling nuisance by the powers-that-be. This is generally how Councils treat ‘average’ citizens who get in the way of business as usual. Here’s a guy who’s offered personally to pay for additional qualified assessment of the present Westshore approach, but has been told, effectively, to ‘get lost’. At the end of this article, I’ve included Larry’s background to indicate he might just be a helluva lot more credible than the Councillors and bureaucrats who are making the decisions on our coastal erosion challenges.
Personally, given what I heard and saw, I found his thumbs-down verdict on Napier’s present course to be rather convincing.
As a counterpoint to the guest post from Larry that I’m publishing below, read first the response the Regional Council staff gave when queried at a Council meeting recently about the status of Westshore. I observed that the staff was quite reluctant to actually discuss the matter when asked in public session; they promised a written response instead (avoiding any public challenge). Here’s what Councillors were sent:
“Recent reports in local newspapers that the renourishment project is failing are not well founded. Localised erosion has however occurred in the vicinity of a concrete ramp placed over the beach crest to enable the surf club to launch surfboats and IRBs. This is a normal effect in the vicinity of localised points of hard protection works.”
Now read Larry Dallimore’s analysis (lengthy, but some things require explaining!), look over his professional background, and decide … Who would you believe?
On Coast Protection
By Larry Dallimore
High seas from an ENE direction are forecast for the HB coastline during three tides on the 30th and 31st March 2011. Swells approaching 2m will peak on the high tides at 03:30pm on Wednesday and 04:00am and 04:30pm on Thursday. The 1.5m neap tides will lessen the effect however the severity of this swell event is dependent on the strength and direction of Cyclone Bune. The offshore storm has entered NZ waters and passed over Raoul Island NE of East Cape and is slowly weakening as it heads south.
These are not severe swells and this is not an extraordinary event. Moderate to high swells will influence HB beaches if it tracks offshore within 400kms of the coast. The effect on our beaches could be significantly reduced if the category 2 cyclone slows and weakens or the high pressure system over central NZ pushes the SE path beyond 600 kms from the NZ coast.
Regarding the Cape Coast, Tom says “have a go at this one folks” … so here is my opinion. The solution for beach erosion from Clifton to Haumoana will be difficult while the HBRC adopts the “Paul Komar Report” as the benchmark for approving a remedy. The HBRC paid two thirds (including the Port’s investment of one third) for this report, which had the desired last paragraph – “it is time to stop blaming the Port structures for coastal erosion”.
There are many baseless findings and omissions in this report but there will be a problem for the Cape Coast while the HBRC accepts Komar’s assessment that 18,000 m3 of greywacke stone enters the Haumoana littoral cell annually due to the erosion of Cape Kidnappers. This source does not exist. The origin of greywacke shingle is in the ranges and logic suggests it was transported via ancient rivers into the Bay to form the seabed beyond the deep water “Springs”. The established seabed was the source of beach replenishment for the Cape Coast, with minimal recent contributions from Tukituki River flooding and the forces of the northerly sediment drift.
The “do nothing” option and “let nature takes its course” is the modern approach, often promoted by persons who are not directly affected or by those fundamentally opposed to enhancement of the environment.
Plus, this could be a reasonable stance considering the numerous marine engineering failures resulting from bad advice and poor decision making. The closest example is the Whakarire Ave Seawall built in 1994 by the NCC, which has caused wave energy to funnel into the south end of Westshore Beach. Instead of removing this problematic seawall, the NCC has applied for Consent to build a $2M offshore breakwater to add another intrusive structure. The consultants have confirmed that strengthening the existing rock protection remains an option. This is an environmentally friendly alternative that will be less than 15% of the cost of a breakwater and it will adequately protect properties in the constantly changing Erosion Zone.
The proposed breakwater, on the other hand, will redirect wave energy further north towards several low-lying properties located behind the weak shingle stopbank. These houses are now more vulnerable to severe swells due to beachhead retreatment. The resultant damage to the beach will be monitored to determine the necessity for hard engineering … but only when the loss of private and public land becomes a priority.
My assessment of man-made erosion at Westshore Beach is well-documented; but there are unique considerations for a solution for the Cape Coast. They include the status of replenishment, the influence of the coastal drift, suitability of protruding groynes compared to a land based seawall and the assessment of capital cost versus asset loss.
A well designed, well constructed and well proven permanent rock seawall could be the only option. All “last resort” hard engineering seawalls built in a wave system have an eddy effect (known as the end effect) requiring the ends to join a headland or a beach in a state of accretion. The popular “rip rap” design built along the entire 5 kms from Clifton to the Tukituki River mouth may be the ultimate solution. An isolated section of seawall is not a practical option within an eroding beach. A capital cost with minimal annual maintenance would be approximately $6M to $8M. Land and infrastructure could remain intact but could eventually be at the expense of an expansive sandy recreational beach.
Westshore has a slightly different problem. A sandy recreational beach is a thing of the past. As recently as July 2010, the consultants finally conceded that the beach is in a state of permanent erosion. The NCC has decided to continue importing unsuitable nourishment shingle in grossly inadequate quantities to counter the current aggressive erosion of the sandy inshore seabed and beachhead.
In 1985, when engineers considered erosion was cyclical and easy to control, nourishment was the best option. However 13 years later in 1998, the consultants presented a 2.85 km seawall as a recommended “hard engineering” option. This recommended solution was discarded because the estimated cost was based on importing rock from New Plymouth and Tauranga. The low maintenance seawall proposal was also documented in Becas Report 2003 at a ridiculous $80M (CPI adjusted to 2010). This option continues to be discredited by all NCC Councillors because they accept flawed advice that rock needs to be imported into a region which has abundant resources of hard limestone rock. The NCC and HBRC engineers refer to the Komar and Becas reports for coastal solutions and the numerous and obvious inconsistencies remain unchallenged.
Many seawalls are highly successful and perform as required; however many groynes and breakwaters have turned into environmental disasters. Around 1980 the first of two groynes was built within 350m of the Port of Napier breakwater at the north end of Marine Parade. The designed purpose was to impede the flow of coastal sediment around the breakwater to limit the infilling of the dredged channel used for ships accessing the Port. This major project was a huge success at impeding the natural northerly drift with vast quantities of sand and shingle accumulating on the southern side and building up back to Pacific Beach.
What the model did not show, but a swell event did, was the scouring effect of the groyne which threatened the foundations of a new workshop on the northern side. The groyne was urgently demolished, plans for the second groyne were shelved and the groyne project was deemed an expensive failure. The remnants of this groyne with a huge gap to allow the shingle to get through remain visible at the Ports southern entrance. It is well depicted on satellite photos.
A huge rock apron, an extensive extension and a deflecting arm on the breakwater have since ensured that the extended and deepened navigational channel is not constantly filled with naturally transported coastal sediment. The 397 page Paul Komars report or the many Beca Infrastructure reports make no reference to these recently constructed impediments to the replenishing sediment that had kept Westshore Beach in a state of accretion up to 1980.
The above references to the Westshore Beach problems are relevant to the Cape Coast situation. WOW needs to question the advice of “so called” experts to ensure an appropriate, practical, and affordable solution gets urgent attention.
Doesn’t sound like a ‘nutter’ to me. How about you? Here’s his background … Tom
- Ministry of Works – Bridge & Roads Dept – Civil Engineering Draughtsman.
- Auckland Regional Authority– Regional Roads Division– Motorway Designer.
- Earthmoving Equipment Ltd – Civil Engineering Contractor – Admin & Project Management.
- Dallimore Groundworks Ltd – Earthmoving & Heavy Haulage & Quarry Operator – Sole Director.
- ‘Retirement’ – Sold up.
- East Coast Contractors Ltd – Contracting & Shingle Plants – General Manager on 3yr Contract.
- ‘Retired’ … again.
- Contracting works for various Govt departments and almost every Council on the East Coast.
- Operated three limestone quarries that supplied 352,000 tonnes of rock for Port works.
- Preferred heavy plant hire contractor to the Port during the period of major development.
- Directly involved in the operation of shingle screening and crushing plants at various sites.
- Supplied all the heavy plant to build the Waimarama seawall which was controlled by the HBCB.
- Supplied all the heavy earthmoving equipment for installing the offshore Hastings sewer pipeline.
- Carried out drainage contracts and river maintenance works for the HB Catchment Board.
- Directly involved in a large seawall contract on the NSW coast and dams in QLD.
Westshore Beach erosion:
- Westshore was my playground and place to swim from mid 1950’s.
- Beachfront resident since the late 1970’s.
- Main heavy plant contractor to the Port between early 1970’s and mid 1990’s.